Servo control system and its control method

ABSTRACT

After a controller # 1  has started giving an interpolating instruction, the length on an interpolation line is calculated by a first calculation means in synchronism with a clock signal from a clock synchronous circuit  45 , and after having executed a first step for generating a synthetic locus-use frame  100  based upon the calculated value, the synthetic locus-use frame  100  is transmitted to controller # 2  so that, after controller # 2  has executed a second step for receiving a synthetic locus calculation-use frame from a receiving means, controllers # 1, #2  execute a third step for calculating the position on the interpolation line based upon the synthetic locus-use frame  100  by using a second calculation means.

TECHNICAL FIELD

The present invention relates to a servo control system having aplurality of servo-controllers, and more specifically relates tointerpolation controlling of respective axes of servo-motors.

BACKGROUND ART

Referring to FIG. 8, a conventional servo control system which isdisclosed in Japanese Laid-Open Patent Publication No. 9-269811, will beexplained.

In FIG. 8, the servo control system is constituted by a host CPU 6 whichoutputs controlling instructions to the entire system as an uppercontrolling unit,

-   -   a plurality of servo-CPUs 8, 9 which executes the same        calculations as the host CPU 6 and serve as lower controlling        unit, drivers D1 to D3 which are connected to the servo-CPU 8        and also connected to servo motors M1 to M3 of an        orthogonal-type robot (Cartesian type robot) 15, and drivers D4,        D5 which are connected to the servo-CPU 9 and also connected to        servo motors M4,M5 of a joint-type robot 17.

To the host CPU 6 are connected a key board 10 through which positionaldata for positioning points, for example, are inputted, an instructiondevice 11 for giving instructions about positional data as topositioning target points, and an external input-output circuit 13 thatallows transmitting and receiving operations to or from an externaldevice.

The following description will discuss an operation of the servo-controlsystem having the above-mentioned arrangement shown in FIG. 8.

Upon starting an interpolation controlling process, the host CPU 6transmits operating instructions for the next target point etc., to theservo-CPUs 8 and 9, and then the servo-CPUs 8, 9 execute the samecalculations respectively for the synchronous control. Based on theresult of the above calculations, the servo-CPUs 8, 9 execute theposition feed-back controlling calculations of the respectiveservo-motors M1 to M3, M4, M5 to transmit positioning completioninstructions to the host CPU 6.

In the above-mentioned servo control system, the respective servo-CPus8, 9 to which operating instructions are transmitted from the host CPU 6can execute the same calculations respectively to carry out thesynchronous control among the robots 15 and 17. Therefore, theabove-mentioned system provides an effective control system forsynchronous control when the number of controlled axes is comparativelysmall.

However, in a servo control system in which a number of motors aresynchronously controlled among the respective servo-CPUs 8, 9 forinterpolation controls, for example, in a servo control system fordriving a tire molding machine with a number of control axes, as will bedescribed later, the calculation time required in the respectiveservo-CPUs 8, 9 increases as the number of motors to be synchronouslycontrolled increases, when each servo CPUs 8 and 9 need to execute thesame calculations. This results in a longer interpolation controllingtime.

In order to solve this problem, utilization of those servo-CPUs 8, 9with a higher processing speed is recommendable, however, there is aninevitable limitation to the processing speed. Here, in the case whenrespective motors are mutually subjected to an interpolation controllingprocess, with respect to multiple axes M1-M5 as shown in FIG. 8, theseare simply shown by two axes form, that is, X-axis and Y-axis as shownin FIG. 9.

In FIG. 9, the interpolation controlling calculations consist ofsynthetic locus calculations for calculating a length Lt1 on aninterpolation line and respective-axis calculations for calculatingpositions Xt1 and Yt1 of the respective axes based on the length Lt1 onthe interpolation line. Since the synthetic locus calculations areexpected to be common to the respective motors, there is no need for therespective servo-CPUs 8, 9 to execute the same synthetic locuscalculations, respectively.

Therefore, it is possible that either one of the servo CPU 8 (9)executes the synthetic locus calculations, and the other respectiveservo CPUs 8, 9 execute respective-axis calculations using the resultantvalue of the synthetic locus calculations.

However, the respective servo CPUs 8, 9 can not execute the respectiveaxis calculations while one of the servo CPU 8 (9) is executing thesynthetic locus calculations, therefore, the total interpolation-controlprocessing time which is the sum of the synthetic locus calculation timeand respective axis calculation time is not substantially reduced.

The present invention has been made to solve the above-mentioned problemin the servo-control system which carries out an interpolation controlof respective axes of motors, and the object of the invention is toprovide a servo control system and a control method thereof which candecrease the interpolation-control processing time of this entire systemamong two or more controllers without using CPU with a higher processingspeed.

DISCLOSURE OF INVENTION

A servo control system according to a first invention is provided with:a first controller which carries out an interpolation-controllingprocess by calculating the length on a first interpolation line based onrespective first axes of the first and second motors, and a secondcontroller which carries out an interpolation-controlling process bycalculating the length on a second interpolation line based onrespective second axes of the third and fourth motors, wherein the firstcontroller includes a first storing means for storing information usedfor calculating the length on the first interpolation line, wherein thesecond controller includes a second storing means for storinginformation used for calculating the length on the second interpolationline, wherein the first and second controllers include a third storingmeans for storing information used for calculating the positions of thefirst and second respective axes based on the lengths on the first andsecond interpolation lines, a first calculating means which, afterinitiation of the interpolation instruction, reads out informationstored in the first and second storing means to calculate the lengths onthe first and second interpolation lines, and which produces a firstframe based on the resultant calculated values, a first transmittingmeans for transmitting the first frame to the other of the controllers,a receiving means for receiving the first frame, and a secondcalculating means which reads out information stored in the secondstoring means to calculate the positions of the respective first andsecond axes based on the lengths on the first and second interpolationlines.

According to such a servo control system, the first and secondcontrollers allow the first calculating means to calculate the lengthson the first and second interpolation lines, and the first frame, formedbased on the calculated value, is transmitted from the first controllerto the second controller as well from the second controller to the firstcontroller by the first transmitting means, and after the first andsecond controllers have received the lengths on the interpolation linesthrough the receiving means, the positions of the respective first andsecond axes are calculated by the second calculation means based on thelengths on the first and second interpolation lines.

Therefore, since after the first and second controllers havesimultaneously calculated the lengths on the first and secondinterpolation lines by the first calculation means, the positions of therespective first and second axes are calculated by the secondcalculation means, it is possible to shorten the interpolationcontrolling time in comparison with a servo control system in which,after the first controller has calculated the length on the firstinterpolation line, the second controller successively calculates thelength on the second interpolation line to calculate the positions ofthe respective first and second axes.

Here, the interpolation controlling time refers to the sum of a time forcalculating the length on the interpolation line and a time forcalculating the positions of the respective axes.

A servo control system according to the second invention ischaracterized in that the first and second controllers in the firstinvention further include: the fourth storing means for storing aninterpolation instruction, a respective-axes instruction generatingmeans which reads out the interpolation instruction from the fourthstoring means based on initiation of the interpolation instruction togenerate instruction values for the respective first and second axes anda second frame based on the instruction values, the second transmittingmeans for transmitting the second frame to the other controller, and thesecond receiving means for receiving the second frame.

According to the servo control system, the respective-axes instructiongenerating means generates the respective-axes instructions forcalculating the positions of the respective axes, and the second frameis transmitted to the other controller so that the first and secondcontrollers are allowed to receive the respective-axes instructions.

Therefore, since the positions of the respective axes are calculated bythe respective axes instruction generating means for each of theinterpolation instructions, it becomes possible to construct aservo-control system by using only the controllers without receiving therespective-axes instructions from upper controllers.

A servo control system according to the third invention is characterizedin that the servo control system according to the first inventionfurther include an upper controller for transmitting an interpolationinstruction to the first and second controllers, wherein the uppercontroller is provided with a respective-axes instruction generatingmeans which generates first and second respective-axes instructionsbased on the interpolation instruction, and transmits the first andsecond respective-axes instructions to the first and second controllers,and the first and second controllers have the third receiving means forreceiving the first and second respective-axes instructions.

According to the third invention, the upper controller allows therespective-axes instruction generating means to generate therespective-axes instructions used for calculating the positions of therespective first and second axes, and transmits these to the first andsecond controllers so that the second controller receives therespective-axes instructions.

Therefore, since the first and second controllers need not to generatethe first and second respective-axes instructions, it is possible toreduce the operation load on the first and second controllers, and theoperation load on the upper controller is also mitigated since it onlyneeds to generate the respective-axes instructions.

According to the fourth invention, a control method for the servocontrol system comprising a first controller which carries out aninterpolation controlling process by calculating the length on the firstinterpolation line based on the respective first axis of the first andsecond motors, and a second controller which carries out aninterpolation controlling process by calculating the length on thesecond interpolation line based on the respective second axes of thethird and fourth motors, includes: a first step, after the first andsecond controllers have started the interpolation instructions,calculating the lengths on the first and second interpolation lines byusing the first calculation means, to generate a first frame based onthe calculated value, a second step of transmitting the first frame fromeither of the first and second controllers to the other controller bythe transmission means, so that the first frame is received by the othercontroller through the transmission means, and a third step ofcalculating the positions of the respective first and second axes basedon the first frame by using the second calculation means in the firstand second controllers.

According to the control method for the servo control system, since thefirst and second controllers simultaneously calculate the lengths on thefirst and second interpolation lines by using the first calculationmeans, and calculate the respective first and second axes positionsbased on the calculated lengths on the first and second interpolationlines, it is possible to shorten interpolation controlling time incomparison with the conventional system in which the first and secondcontrollers calculate sequentially the length on the first interpolationline and the length on the second interpolation line.

The control method of the servo control system according to the fifthinvention is characterized in that the first to third steps according tothe third invention are executed after the first and second controllersallowed the respective-axes instruction generating means to generate theinstruction values of the respective first and second axes based on thestart of the interpolation instruction, and after having transmitted thesecond frame formed based upon the instruction values of the respectiveaxes to the other controller.

According to the control method, a servo control system can be builtonly by controllers, without receiving respective axial instructionsfrom an upper controller, since the respective axial instructiongenerating means calculates the respective axial position for everyinterpolation instruction.

The control method of the servo control system according to the sixthinvention is characterized in that the first to third steps according tothe fourth invention are executed after an upper controller generatedthe instructions for the respective first and second axes based on thestart of the interpolation instruction, and after having transmitted theinstruction for the respective first and second axes to the first andsecond controllers.

According to the control method of the servo control system, there is noneed for the first and the second controllers to generate the respectiveaxes instructions. Therefore, the calculations load of the first andsecond controllers is mitigated and the calculations load of the uppercontroller is also effectively reduced, since it only generatesrespective axes instructions.

A servo control system according to the seventh invention ischaracterized in that the first frame according to the first or secondinvention includes a reaching instruction that is generated when apredetermined range of the previous positioning instruction position hasbeen reached based on the calculated values of the respective first andsecond axes.

According to the servo control system, the next positioning instructioncan be effectively generated in accordance with the reaching instructionbased on the calculated values of the respective first and second axes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic front view of the tire molding equipment which isdriven and controlled by a servo control system in accordance with oneembodiment of this invention;

FIG. 2 is a block diagram of the entire servo control system showed inFIG. 1;

FIG. 3 (a) is a block diagram showing the synthetic locus calculationframe which is used in the system shown in FIG. 2;

FIG. 3 (b) is a block diagram of a frame for respective axescalculation;

FIG. 4 is an explanatory curve showing an interpolation controllingprocess which is executed by the servo control system shown in FIG. 1,in which positioning points P0, P1, P2, P11, P12 are indicated on aplane defined by the X-Y axes;

FIG. 5 is a flow chart showing a process in which a target is shifted topositioning points shown in FIG. 4 by using the servo control system ofFIG. 1;

FIG. 6 is a time chart showing a process in which a target is shifted topositioning points, P0, P1, P2, Pl1, P12 shown in FIG. 4, by using theservo control system of FIG. 1;

FIG. 7 is a block diagram showing the entire constitution of a servocontrol system according to another embodiment of this invention;

FIG. 8 is a schematic diagram showing the entire constitution of theconventional servo control system;

FIG. 9 is a curve showing the positioning points P0, P1, and P2.

BEST MODE FOR CARRYING OUT THE INVENTION Embodiment 1

Referring to FIG. 1 to 4, a servo control system according to anembodiment of the present invention will be explained. FIG. 1 is aschematic front view of the tire molding equipment in which drivecontrol is carried out by a servo control system according to thisinvention. FIG. 2 is a block diagram showing the entire servo-controlsystem for driving the tire molding equipment showed in FIG. 1. FIG.3(a) is a block diagram showing the synthetic locus calculation frameused for the system of FIG. 1. FIG. 3(b) is a block diagram of therespective-axes calculation frame. FIG. 4 is a curve that shows aninterpolation controlling process executed by the servo control systemof FIG. 1, which includes positioning points P0, P1, P2, P11, P12 on theX-Y axis plane.

In FIG. 1, a tire molding apparatus 20 for molding a tire using a servocontrol system is provided with a servo motor M1 for rotating a drum 21which forms a tire and which is placed in the center; an A materialsupplying device 22 for supplying a tire forming material at theleft-hand side of the drum 21 from a viewpoint facing to the drawing;and a B material supplying device 24 for supplying a tire formingmaterial at the right-hand side of the drum 21. The A material supplyingdevice 22 in the left-hand side comprises a first material supplyingunit and a second material supplying unit. The first material supplyingunit is provided with belt-conveyers B2, B3 by which the material a issupplied and which is driven by servo motors M2, M3, and a guidingbelt-conveyer B6 which is located in the neighborhood of the dram 21 andhaving the servo motor M6. The second material supplying unit isprovided with belt-conveyers B4, B5 by which the material b is suppliedand which is driven by servo motors M4, M5. The B material supplyingdevice 24 in the right-hand side comprises a third material supplyingunit and a fourth material supplying unit. The third material supplyingunit is provided with belt-conveyers B8, B9 by which the material c issupplied and which is driven by servo motors M8, M9, and a guidingbelt-conveyer B7 which is located in the neighborhood of the dram 21 andhaving a servo motor M7. The fourth material supplying unit is providedwith belt-conveyers B10, B11 by which the material d is supplied andwhich is driven by servo motors M10, M11.

In order to supply the tire materials a to d to the dram 21, the tiremolding apparatus 20 is designed in such a manner that the servo motorsM2 through M6 and M8 through M11 which constitutes the above-mentionedmaterial supplying units, the servo motor M1 of the dram 21, and theservo-motors M6 (M7) of the guiding belt-conveyers B6 (B7) aresynchronously controlled properly each other (interpolation-controlled).

Here, in general, the tire molding apparatus 20 uses approximately 20kind of materials, and about 100 axes in most cases, but FIG. 1 showsonly a simplified structure. In FIG. 2, the servo control system 25 isprovided with controllers #1 to #3 which is connected to a bus 30 anddrive servo motors M1-M11. The controller #1 serving as the firstcontroller is connected to servo motors M1 to M4 through the servodrivers 71 a to 71 d, the controller #2 serving as the second controlleris connected to servo motors M5 to M8 through the servo drivers 72 a to72 d, and the controller #3 is connected to servo motors M9 to M11through the servo drivers 73 a to 73 c.

Thus, in order to carry out the synchronous control (interpolationcontrol), the respective axes of the servo motors M2 to M5 and M8 to M11which form the respective material supplying units, the servo motor M1of the drum 21, and the servo motor M6 (M7) of guide-use belt-conveyorB6 (B7) are constituted so that predetermined controlling operation arecarried out between controller #1 and controller #2 (#3). Respectivecontrollers #1 to #3 are provided with bus-control-use I/Fs 31 to 33that are connected to a bus 30, CPUs 41-43 which are connected to theI/F 31-33 through interrupt control circuits 35 to 37, clock synchronouscircuits 45 to 47 which are connected to bus-control-use I/Fs 31 to 33and serving as a clock generating means for generating clock signalswith a constant cycle, memory 51 to 53 connected to CPUs 41-43, andcommunication-use I/F 61-63. The respective servo drivers 71 a to 71 d,72 a to 72 d, and 73 a to 73 d are connected to the communication-useI/F 61 to 63. Memory 51 to 53 are respectively provided with syntheticlocus calculation unit 51 b serving as the first storing means,synthetic locus calculation units 52 b, 53 b serving as the secondstoring means, respective axes calculation units 51 c to 53 c serving asthe third storing means, and control instruction units 51 a to 53 aserving as the fourth storing means.

In FIG. 4, the interpolation control on respective axes consists of thesynthetic locus calculations for calculating the length Lt1 and Lt11 onthe interpolation line, and the respective axes calculations forcalculating positions Xt1, Yt1 on the first respective axes (oninterpolation line) based on the length Lt1 on the interpolation lineand for calculating positions Xt1 and Yt11 on the second respective axes(on interpolation line) based on the length Lt11 on the interpolationline. The control instruction unit 51 a stores a starting position(current value) P0 serving as an interpolation instruction, targetpositions P1, P2, a maximum speed value, an acceleration time, and adeceleration time. The control instruction unit 52 a stores a startingposition (current value) P0 serving as an interpolation instruction,target positions P11, P12, a maximum speed value, an acceleration time,and a deceleration time.

Furthermore, the control instruction units 52 a stores a startingposition (current value) P0 serving as an interpolation instruction,target positions P21 and P22 (not shown) a maximum speed value, anacceleration time, and a deceleration time. The synthetic locuscalculation unit 51 b stores parameters such as a total shift distance,a speed, an acceleration time, and a deceleration time, so as to carryout the synthetic locus calculations used as information on theinterpolation line between a starting position P0 and target positionsP1, P2. The unit 51 b also stores a predetermined interpolationcalculation expression and a calculated synthetic locus calculationvalues. The synthetic locus calculation unit 52 b (53 b) storesparameters such as a total shift distance, a speed, an accelerationtime, and a deceleration time, so as to carry out the synthetic locuscalculations used as information on the interpolation line between astarting position P0 and target positions P11 (P12), P12 (P22), and theunit 52 b (53 b) also stores a predetermined interpolation calculationexpression and a calculated synthetic locus calculations values. Each ofthe respective axes calculation units 51 c to 53 c stores informationsuch as a current position, a total shift distance and a total shiftamount of each axis. Moreover, each of the units 51 c to 53 c alsostores a predetermined interpolation calculation expression andcalculated respective axial calculation values.

FIG. 3(a) shows a format of the synthetic locus frame 100 serving as thefirst frame which is transmitted between controllers #1 to #3, forexample, synthetic locus calculation value calculated by a controller #1is transmitted to the other controllers #2 and #3.

A synthetic locus frame 100 comprises ID101 which has the identificationnumber for identifying controllers #1 to #3, point number 103 whichshows the interpolation stage by defining points P0 to P1 as a number 1and points P1 to P2 as a number 2, an instruction type 105 that shows acontrolled state and consists of an in-position instruction 105 a and acontrol completion instruction 105 b, wherein the in-positioninstruction 105 a serves as a reaching instruction that is generated byreaching a predetermined range in the previous positioning instructionposition, for example, and a synthetic locus calculation value 107.

FIG. 3 (b) shows a format of the respective axes calculation frame 200as the second frame transmitted between controllers #1 to #3. Forexample, the instructions for executing the respective-axes calculationstored in control instruction unit 51 a of controller #1 are transmittedto other controllers #2 and #3. The respective-axes calculation frame200 comprises controllers #1- to #3, point number 203 which is the sameas the point number 103 mentioned above, a control type 205 which showslinear interpolation, circular interpolation, etc., an interpolationtarget axis 207 which specifies servo motors M1, M6, for example, as atarget used for an interpolation operation, and a total shift amount 209used as the distance between the positioning points of the respectiveaxes and total shift amount 211 of each of the X and Y axes. The totalshift amount 209 of controller #1 generates the distance between thefirst point P0 and the points P1 and P2 with respect to positioningpoints of the respective axes to specify servo-motors M1, M6 as theinterpolation target axis 207.

On the other hand, the total shift amount 209 of controller #2 generatesthe distance between the first point P0 and the points P11 and P12 withrespect to positioning points of the respective axes to specify servomotors M4, M5 as the interpolation target axis 207.

Referring to FIGS. 1 to 6, the following description will discuss anoperation for driving a tire molding machine using the servo-controlsystem mentioned above. FIG. 5 is a flowchart that shows the operationof the servo control system shown in FIG. 1, and FIG. 6 is a time chartthereof.

In the tire molding apparatus 20, the drum 1 and belt conveyors B4, B5,B6 are synchronously operated each other, and in addition to thissynchronous operation, the belt conveyors B10 and B11, and the beltconveyors B8 and B9 are also synchronously operated respectively. Here,an explanation will be given of a simplified case in which theservo-motors M1, M6 serving as the first and second motors and theservo-motors M4, M5 serving as the third and fourth motors aresynchronously controlled between the respective controllers #1 and #2.In the case when the servo-motors M1, M6 for driving the drum 21 and thebelt conveyor B6, as well as the servo-motors M4, M5 for driving thebelt conveyors B4, B5, are synchronously controlled between therespective controllers #1 and #2, the first respective axes(corresponding to the X axis) of the servo-motors M1, M5 arerespectively rotated with predetermined amounts, while the secondrespective axes (corresponding to the Y axis) of the servo-motors M6, M4are respectively rotated with predetermined amounts; therefore, as shownin FIG. 4, the synchronous control of this type may be regarded asinterpolation control.

Therefore, an explanation will be given on the assumption that, as shownin FIG. 4, the servo-motors M1, M4, M5, M6 are controlled to shiftpositioning points from P0 to P2 through P1, and from P0 to P12 throughP11 on the biaxial plane of the X and Y axes.

Referring to FIGS. 1 to 6, the operation of the servo-control systemmentioned above will be explained below. Here, calculation clocks areinputted to the bus-control-use I/Fs 31 to 33 by the clock synchronouscircuits 45 to 47.

When, at time t1, a starting instruction for interpolation is inputtedto each of controllers #1, #2 from an external device (not shown) (step201), the CPUs 41, 42 of controllers #1, #2 generate respective-axescalculation-use frames 200 for calculating the respective-axesinstructions for points P1, P11 based upon stored information from thecontrol instruction units 51 a, 52 a (respective-axes instructiongenerating means, step S203). At time t2, the CPU 41(42) transmits therespective-axes calculation-use frame 200 to the bus-control-use I/F31(32)→>the bus 30→the bus-control-use I/F 32(31) (the secondtransmission means, step S205), and the CPU 42(41) of controllers #2, #1receives the respective-axes calculation-use frame 200 through thebus-control-use I/F 32 (31) as a slave process (the second receivingmeans), and stores this in the respective-axes calculation unit 52 c(51c) of the memory 52(51) (step S221).

At time t3, the CPU 41(42) of controllers #1, #2 activates aninterpolation control signal serving as an interpolation instruction sothat an interrupt signal is generated from the interrupt control circuit35(36) to transmit the interrupt signal to the bus-control-useI/F31(32)→bus30→bus-control-use I/F 32(31) (step S207). The CPU 42(41)of controller #2 (#1) receives the interrupt signal through thebus-control-use I/F 32(31) as a slave process (step 223), and determineswhether or not the corresponding axis is managed by its own controller#1, #2 through the interpolation target axis 207 of therespective-axescalculation-use frame 200 (step S225). When the axis is managed by itsown controller #1, #2, a flag for making the respective-axescalculation-use frame 200 of the respective-axes calculation unit 51c(51 c) of the memory 51(52) effective is set to 1 (step S209, S227), itis determined whether or not the respective-axes calculation-use frame200 is effective (step S211, S229).

Here, since this is effective, at time t4, the CPU41(42) of controller#1(#2) functions as the first calculation means in synchronism with thecalculation clock (clock signal) of the clock synchronous circuit 45,that is, it obtains a shift distance Lt1 (Lt11) of a synthetic locus asa length on the interpolation line between points P0-PL (P0-P11) at thecurrent time, and in accordance with the controlling state of theinterpolation, for example, by the fact that the target has reached apredetermined range in the previous positioning instruction position,the in-position instruction 105 a, etc. are set, and the syntheticlocus-use frame 100 containing a synthetic locus calculated value isgenerated (first step, step S213).

At time t5, the CPU 41(42) of controller #1(#2) transmits this tobus-control-use I/F 31(32)→>bus 30→>bus-control-use I/F 32(31) (firsttransmission means, step S215), and the CPU 42(41) of controller #2 (#1)receives the synthetic locus-use frame 100 through the bus control useI/F32 (31) and executes the second step, and reads out the syntheticlocus use frame 100 from the bus control use I/F 32, and stores this inthe synthetic locus calculation unit 52 b (51 b) in the memory 52 (51)(step S231).

At time t6, the CPU41, (42) of controllers #1, #2 functions as a secondcalculation means, that is, calculates to determine the coordinates ofX, Y axes managed by controllers #1, #2, by using the shift distance Lt1(Lt11) of the synthetic locus between point P0-P1(P0-P11) and therespective-axes calculation-use instruction stored in therespective-axes calculation unit 52 b (52 b) of the memory 52(51) (thethird step, step S217, S233). Controllers #1, #2 repeatedly execute theabove-mentioned steps S201 to S237 until the completion of theinterpolation control, thereby completing the interpolation process(step S219, S235), and a flag which nullifies the respective-axescalculation-use frame 200 of the respective axes calculation unit 51 c(51 c) of the memory 51 (52) is set to 0 (step S221, S237), therebycompleting the operation. The respective-axes calculation-use frame 200is generated by controllers #1, #2 for each point, and therespective-axes calculation-use frame 200 of points P2, P12 areback-ground processed, calculated before the start of control of pointsP2, P12, and transmitted to controllers #1, #2.

Moreover, at the time of deceleration and stop, the in-position signal105 a serving as the reaching instruction for executing the in-positionprocess is set in the instruction type 105 so that, during the time fromthe start of deceleration and stop to the positioning to each point, thecomposite locus-use frame 100 is transmitted to controller #2, and therespective controllers #1, #2 are allowed to execute the process at thetime of deceleration and stop in addition to the respective-axescalculations.

In a servo-control system 25 having servo-motors M1, M6 and servo-motorsM4, M5 that are interpolation targets between these differentcontrollers #1, #2, the synthetic locus calculation Lt1 forinterpolation controlling so as to set point P0→P1 in controller #1 andthe synthetic locus calculation Lt1 for interpolation controlling so asto set point P0→P1 in controller #2 are simultaneously executed, and thesynthetic locus calculation value Lt1 of controller #1 is transmitted tocontroller #2 while the synthetic locus calculation value Lt11 istransmitted to controller #1.

Thus, controllers #1, #2 are able to carry out respective axescalculations based upon synthetic locus calculation values Lt1, Lt11, sothat it becomes possible to shorten the processing time of interpolationcontrol as the servo-control system 25.

In other words, in the case when the same interpolation controlcalculation is carried out by the respective controllers #1, #2 as inthe conventional case, the interpolation controlling time is set to 15μsec×2+2.5 μsec 32.5 μsec, supposing that the execution time of thecomposite locus calculation is 15 μsec and the execution time of therespective-axes calculation is 2.5 μsec, while the interpolationcontrolling time of the servo-control system 25 of the present inventionis 15 μsec+2.5 μsec=17.5 μsec. The ratio k of the interpolationcontrolling times is indicated as follows:

-   -   K=17.5/32.5=0.54

Therefore, in the servo-control system 25 of the present embodiment, theinterpolation controlling time is reduced to approximately half theconventional interpolation controlling time.

Preferred Embodiment 2

Referring to FIG. 7, the following description will discuss anotherpreferred embodiment of the present invention. As shown in FIG. 7, anupper controller 101 is installed in the servo-control system 25, andthe upper controller 101 may have functions corresponding to controlinstruction units 51 a to 53 a in memories 51 to 53 installed in therespective controllers #1 to #3 of FIG. 2, functions for transmittinginterpolation instructions to controllers #1 to #3, and functions of therespective-axes instruction generating means for generating therespective axes instructions by using interpolation instructions and fortransmitting these instructions to controllers #1, #2.

In accordance with such a servo-control system 25, the processes carriedout in step S203 and S205 in FIG. 5 can be executed by the uppercontroller 101 in a substituting manner.

INDUSTRIAL APPLICABILITY

As described above, the servo-control system and its controlling methodof the present invention are suitably applied to, for example, a tiremolding apparatus.

1. A servo-control system, comprising: a first controller which controlsa first and third shafts; a second controller which controls a secondand fourth shafts; wherein said first controller includes a firststoring means in which information used for calculating the length on afirst interpolation line is written, a first calculation means forreading the information from said first storing means to calculate thelength on said first interpolation line, a transmitting means, and areceiving means, said second controller includes a second storing meansin which information used for calculating the length on a secondinterpolation line is written, a second calculation means for readingthe information from said second storing means to calculate the lengthon said second interpolation line, a transmitting means, and a receivingmeans, and said first and second controllers transmit or receivemutually the lengths on said first interpolation line and secondinterpolation line through said transmitting means or receiving means,whereby calculating the positions of said first and second axes basedupon the length on the first interpolation line, and calculating thepositions of said third and fourth axes based upon the length on thesecond interpolation line.
 2. A servo-control system according to claim1, wherein the calculation of the length on the first interpolation lineby said first calculation means is simultaneously executed with thecalculation of the length on the second interpolation line by saidsecond calculation means.
 3. A servo-control system according to claim1, wherein said first and second controllers further comprise a fourthstoring means respectively, the fourth storing means in said firstcontroller stores information needed for interpolation instruction forsaid first and second axes, which includes a current position, a targetposition, a maximum speed value, an acceleration time, and adeceleration time, the fourth storing means in said second controllerstores information needed for interpolation instruction to said thirdand fourth axes, which includes a current position, a target position, amaximum speed value, an acceleration time, and a deceleration time, thefirst and second controllers generate respectively respective-axiscalculation frame every target position based upon the information fromsaid fourth storing means to transmit or receive mutually the respectiveaxis calculation frame before said target position control starts.
 4. Aservo-control system according to claim 1, wherein said first and secondcontrollers transmit or receive mutually an in-position instruction andan instruction type, along with the length on the first or secondinterpolation line, wherein the in-position instruction serves as areaching instruction that is generated by reaching a predetermined rangein the previous positioning instruction position and wherein theinstruction type shows a controlled state including a control completioninstruction.
 5. A servo-control system according to claim 1, whereinsaid first and second controllers further comprise an upper controller,the upper controller containing information needed for interpolationinstruction to the first and second axes, including a current position,a target position, a maximum speed value, an acceleration time, anddeceleration time; and information needed for interpolation instructionto the third and fourth axes, including a current position, a targetposition, a maximum speed value, an acceleration time, and decelerationtime; the respective-axis calculation frame being generated based uponsaid information to transmit to said first and second controllers.
 6. Acontrol method of a servo-control system using a first controller whichcontrols a first and third shafts and a second controller which controlsa second and fourth shafts, and mutually controlling between said firstand second controllers, comprising the steps of: executingsimultaneously a synthetic locus calculation needed for respective axescalculation for said first and second axes in said first controller anda synthetic locus calculation needed for respective axes calculation forsaid third and fourth axes in said second controller, transmitting theresult of said synthetic locus calculation in the first controller tothe second controller, transmitting the result of said synthetic locuscalculation in the second controller to the first controller, andexecuting respective axes calculation for said first to fourth axesbased upon the result of said synthetic locus calculations.